1. Field of the Invention
The present invention generally relates to a method for fabricating devices on semiconductor substrates. More specifically, the present invention relates to a method of etching magnetic and ferroelectric materials.
2. Description of the Related Art
Microelectronic devices are generally fabricated on a semiconductor substrate as integrated circuits wherein various conductive layers are interconnected to one another to facilitate propagation of electronic signals within the device. An example of such a device is a storage element in magneto-resistive random access memories (MRAM) or ferroelectric random access memories (FeRAM).
MRAM and FeRAM comprise a plurality of memory cells that are interconnected to one another to facilitate storage of digital information. In MRAM, digital information is stored in a form of the direction of magnetization of a magnetic material, and in FeRAM the information is stored in the form of the direction of polarization of a ferroelectric material.
A memory cell in a MRAM device is a multi-layered structure comprising a pair of magnetic layers separated by a tunnel layer of a non-magnetic dielectric material (e.g., aluminum oxide (Al2O3) and the like). The magnetic layers may each comprise a plurality of films of magnetic materials, e.g., permalloy (NiFe), cobalt iron (CoFe), and the like, as well as film electrodes forming an electrical connection for the memory cell to the lines of the MRAM. In a FeRAM device, a memory cell comprises a layer of ferroelectric material, such as, e.g., lead zirconate titanate (Pb(ZrTi)O3, or PZT), barium strontium titanate (Ba(SrTi)O3), or BST), and the like that is supplied with film electrodes to form a capacitive structure.
Fabrication of MRAM or FeRAM devices comprises etch processes in which one or more layers comprising a device film stack are removed, either partially or in total. MRAM and FeRAM film stacks comprise the layers that are formed from materials that may be easily oxidized, sensitive to corrosion or easily damaged by plasma. During etching of these materials, the materials may leave difficult to remove conductive post-etch residues upon the film stack. Such residues may build up along the sides of the film stack. The conductive residues or eroded layers may cause electrical short-circuits within the MRAM or FeRAM device.
During etching the MRAM or FeRAM film stack, the conductive residues are repeatedly removed using wet cleaning processes that clean the wafer in solvents comprising, in various combinations, hydrogen fluoride (HF), ammonium fluoride (NH4F), ammonium hydroxide (NH4OH), hydrogen peroxide (H2O2), and the like. Such cleaning processes are disclosed, for example, in commonly assigned U. S. patent applications Ser. No. 10/218,244, filed Aug. 12, 2002 and Ser. No. 10/231,620 filed Aug. 29, 2002, which are incorporated herein by reference. The disadvantage of the wet cleaning processes are low efficiency and productivity of such processes, lack of real time (i.e., in situ) end point detection, as well as a need in dedicated equipment that may be incompatible with vacuumed plasma etch reactors used during fabrication of the MRAM device.
Therefore, there is a need in the art for an improved method for etching magnetic and ferroelectric materials that forms less residue on the film stacks during the etching process.